Detecting Improvised Explosive Devices in Urban Areas

Wednesday, April 01 2009

Improvised explosive devices (IEDs) are rudimentary bombs that generally consist of commonly found non-military materials. Although common IED threats include roadside bombs, suicide bombers are another emerging problem in the IED arena. Suicide bombers carrying personal-borne IEDs (PBIEDs) are extremely hard to detect or stop. Because no IED emplacement is necessary, a suicide bomber can quickly strap on an IEDladen vest and move to the kill zone. Placed in the proper urban environment, this weapon is capable of inflicting serious structural damage and killing hundreds of people in mere seconds.

Research has been done to detect magnetic materials used in IEDs in urban environments using a wireless sensor network. Using the magnetic detectors in the wireless sensor nodes, magnetic behaviors and patterns are analyzed to differentiate a person carrying an IED and a person possessing magnetic material like jewelry or keychains. Using wireless sensor nodes instead of standard metal detectors enables the detectors to remain hidden to outside observers. The small nodes easily blend into the indigenous environmental settings to provide stealth.

All IEDs require a power source to initiate the weapon. Most initiators are battery- operated electrical devices, but there are other means of initiation. Spring-loaded initiators require no electrical power to function. The IED initiator detonates the weapon and begins the bombing sequence. Common initiators are blasting caps and fuse igniters. Electrical initiators can be triggered in various ways, including a button, radio frequency, and optical. The IED switch arms the weapon after the initiator sequence begins. The switch could be an arming switch, fuse, or both for redundancy. Once the IED is armed, the internal circuit is complete and detonation occurs shortly thereafter.

One of the first solutions to detect IEDs was to detect the frequency spectrum used by the IED initiator devices. By correctly analyzing the frequency spectrum used by the remote triggers, troops successfully jammed the frequencies and prevented IEDs from being triggered. Electromagnetic pulse jamming also destroyed IED circuitry.

Unmanned Aerial Vehicles (UAVs) use mounted cameras to take pictures of probable IED areas and then come back for more images. The Buckeye camera mounted on a UAV uses an electro-optical sensor capable of producing threedimensional images. Using imagery software or the human eye, the pictures are analyzed against pictures from the same area, but taken at a different time. Scrutinizing the images to the nearest pixel, experts can determine if suspicious IED activity has occurred in a region.

Magnetic Wireless Sensor Networks

A wireless sensor network (WSN) is formed from a series of wireless network nodes or motes, generally in an ad-hoc configuration. Each node contains a small processor to handle sensing duties. Nodes are able to relay information using a predetermined routing protocol such as ZigBee. Due to the wireless constraints, each WSN node needs a self-contained power source such as batteries.

A standard WSN uses the nodes for their physical sensing capabilities in conjunction with a base station, which receives information from the nodes and passes it to another source to process the data. Since the base station receives input from the WSN nodes, it has higher power requirements and must always coordinate data delivery out of the network. Each node contains sensing capabilities appropriate for the network application and needs. Nodes cannot process or analyze the information, but can forward information to either another node or the base station.

The mesh-networking feature of the motes allows them to communicate with each mote in the network. Additional motes can be added to the network or motes can be removed from the network seamlessly. The magnetic detection capability within the motes uses a twoaxis magnetic field sensor to detect electronic voltage perturbations around the sensor. The passive infrared sensors detect dynamic changes in the thermal radiation environment within immediate vicinity of the sensor. The mote also contains a dormant microphone to detect acoustic changes within its environment. Each mote contains four magnetic and passive infrared sensors placed within a cubicle housing to provide nearly 360-degree coverage.